Preheat the oven to 350 degrees F. Line a baking sheet (or 2) with parchment paper.
Place half of the oats in a food processor and pulse until the oats are chopped up, some flour-like, but some pieces remaining. In a bowl, combine all of the oats, flour, baking soda, cinnamon, cardamom, nutmeg and salt. Whisk together.
In a large bowl, whisk together the melted butter and brown sugar until smooth. Whisk in the egg and egg yolk, then the vanilla, until smooth and combined. Take a large spoon and stir in the dry ingredients, mixing until a dough forms.
Scoop the dough out using an ice cream scoop (you want about 2 tablespoons of dough) and place on the parchment paper 2 inches apart. I put 6 on a baking sheet – because they will spread! Bake for 12 to 14 minutes, or until golden on the edges and thin and chewy. Remove and let cool completely.